1. The Field of the Invention
The present invention relates to a passive (no external power input required) apparatus useful for enhancing (increasing) geothermal fluid production from a weak (low pressure) wells by using strong (higher pressure) wells.
2. The Relevant Technology
In geothermal hot water flash (brine or two-phase) systems, multiple wells flow into a fluid gathering system (pipelines) to feed a steam turbine driven electric power plant. The production pressure at the surface in some of the wells may be declining or weak, and produce at marginal rates or not at all if the gathering system pipeline pressure (back-pressure) is too high to allow the required flow. To decrease this back-pressure, the strong wells are often throttled back to allow flow from the weak wells resulting in decrease fluid production from the strong wells. This throttling process reduces the system back-pressure allowing the weaker wells to flow into the pipeline, but curtails production from the strong wells. At some point, as the pressure in the underground reservoir declines with cumulative production, the weaker wells will cease to flow.
Normally, new wells are drilled to make up for the production short-fall. Alternatively, a larger pipeline or a separator station and brine lines are installed on two-phase flash systems to reduce the pressure loss thus allowing the weaker wells to enter the system. Larger diameter, two-phase flow lines can be a concern since oversized pipes can result in flow instability such as dangerous slugging conditions. Separator stations can be used but are very expensive especially if brine transfer pumps are required.
Geothermal two-phase wells will cease to produce fluid when the flowing pressure declines below the maximum shut-in pressure at the well-head. For each psi (pounds per square inch) reduction in effective flowing back-pressure, an increase of 2% to 15% in the total mass flow rate from the lower pressure wells can be obtained. This bonus capacity, in conjunction with keeping the weak wells flowing, can delay supplemental drilling. Geothermal wells cost from $1,500,000 to $3,000,000 to drill and complete. In some geothermal hot water flash fields, up to one-third (1/3) of the original production wells are shut in due to high production pressures (high back pressure).